[Int-area] draft-chroboczek-int-v4-via-v6-02 - "IPv4 routes with an IPv6 next hop"

[Warren Kumari <[e-mail]>]

Hi there,

Doc: draft-chroboczek-int-v4-via-v6 - "IPv4 routes with an IPv6 next hop"
<https://datatracker.ietf.org/doc/draft-chroboczek-int-v4-via-v6/>

Back in August 2022, when draft-ietf-babel-v4viav6 was going through IESG
eval, I raised the concern that something this fundamental (and, frankly,
awesome :-)) deserves to be documented in a separate, standalone document,
so that it can be more fully discussed, and, more importantly, referenced
cleanly in the future. We wrote this document to do just this….

Normally, when one thinks of an IP route, you automatically assumes that
the next-hop will be the same protocol as the prefix  (e.g: 192.0.2.0/24
next-hop 10.0.0.1). There is, however, no requirement that this is the case
— you can have an IPv6 next-hop for an IPv4 prefix (e.g: 192.0.2.0/24
next-hop 2001:DB8:1:1::1) - the router doesn't care, it just wants to
figure out the outgoing interface and (generally) MAC address to send it
to.

This means that you can have an IPv6-only "core" network, passing IPv4
traffic. This all basically "Just Works", but it isn't really described
anywhere, and many CLIs and tools don't allow it (again, probably because
of assumptions).

We'd really appreciate review and feedback — again, this isn't documenting
a major "change", but more noting this the design of command lines,
tooling, etc  should allow it.

W
P.S: While writing  this email, I noticed that we should also reference RFC8950
- "Advertising IPv4 Network Layer Reachability Information (NLRI) with an
IPv6 Next Hop" <https://datatracker.ietf.org/doc/rfc8950/> — I'm sure that
there are many other related documents that we've also forgotten to
reference...

W